Simplify the following expression: $a = \dfrac{1}{9p} + \dfrac{3}{7p}$
In order to add expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $9p$ and $7p$ $\lcm(9p, 7p) = 63p$ $ a = \dfrac{7}{7} \cdot \dfrac{1}{9p} + \dfrac{9}{9} \cdot \dfrac{3}{7p} $ $a = \dfrac{7}{63p} + \dfrac{27}{63p}$ $a = \dfrac{7 +27}{63p}$ $a = \dfrac{34}{63p}$